Effects of superimposed dual-frequency (13.56/2 MHz) inductively coupled plasma source on the uniformity of Ar/CF₄ plasma

As one of the methods for controlling the plasma uniformity, superimposed dual frequencies of 13.56 and 2 MHz were used on an inductively coupled plasma (ICP) source, and the effects of the superimposed dual-frequency ICP on the plasma and etch uniformities were investigated and compared with a conventional single-frequency ICP operation at 13.56 MHz using Ar/CF₄. The superimposed dual-frequency ICP operated at 13.56 and 2 MHz improved the plasma uniformity compared to the single-frequency ICP for both Ar and Ar/CF₄ by improving the plasma density near the center region of the wafer close to the edge region. In addition, for Ar plasma, a change in the power ratio of 2/13.56 MHz during the superimposed dual-frequency operation changed the EEDF of the plasma and the IED toward the wall. When SiO₂ was etched using Ar/CF₄ with the superimposed dual-frequency ICP while biasing the substrate with a separate radio frequency power of 12.56 MHz, similar to the results on the plasma uniformity, the SiO₂ etch uniformity within a 300 mm diameter wafer was improved by using the superimposed dual-frequency ICP operated at 13.56 and 2 MHz, as compared to that using a single-frequency ICP of 13.56 MHz.